Chemicals microbial fermentation routes

TABLE 3.3 Potential Routes to Commodity Chemicals by Microbial Fermentation of Glucose... 

Hydroxypropionic Acid (3-HPA). Like the structurally isomeric lactic acid, 3-HPA constitutes a three-carbon building block with the potential of becoming a key intermediate for a variety of high-volume chemicals malonic and acrylic acids, methacrylate, acrylonitrile, 1,3-propanediol, and so forth.Thus, Cargill is developing a low-cost fermentation route by metabolic engineering of the microbial... 

In this chapter, major routes for the production of bulk chemicals from biomass components including carbohydrates, oils, proteins and minor constituents will be identified. These major production pathways rely on microbial fermentation, enzymatic transformation and green chemical extraction or synthesis. 

Lactic acid can be produced by microbial fermentation or by chemical syntiiesis. The main biotechnological routes are based on biomass as a renewable source for production. 

More recently, Glaxo SmithKline patented an efficient fermentation rente for the biosynthetic prodnetion of thymidine (thymine-2-desoxyriboside). Key to the invention is a recombinant strain that efficiently produces high titers of thymidine by blocking some enzymes in the thymidine regulating pathway. This microbial process has now replaced the chemical route and has enabled gsk to supply the anti-AIDS drug AZT (zidovudine) to third-world countries at low cost. 

Succinic acid is a potential platform chemical that is expected to be commercialised in a few years. Although the production capacity of petrochemically derived succinic acid is on the scale of 15 000 tonnes per year (Zeikus etal., 1999), the production capacity of succinic acid derivatives is over 270 000 tonnes per year (Willke and Vorlop, 2004). Fermentative production of succinic acid could offer a viable route to bulk chemical production. Figure 4.4 presents potential routes for chemical production from succinic acid (McKinlay et al., 2007). Another advantage of succinic acid microbial production is the simultaneous requirement for CO2 consumption, which reduces the emission of the most important greenhouse gas and makes fermentative succinic acid production a process of significantly low environmental impact. 

Most studies on microbial exopolysaccharides production have been performed so far using batch fermentation conditions and polymer macromolecules are recovered from fermentation broths by simple chemical and physical techniques, e.g. precipitation and centrifugation. In Scheme 7.2 the route of production of alginate is presented [8]. Some attempts have been made to apply immobilized-cell cultures to the production of alginate and other bacterial polysaccharides. Immobilization techniques are likely to allow the permanent separation of microbial cells from the incubation broth. In the last few years, however, membrane processes have been increasingly used to separate microbial cells from the production medium. A number of studies have therefore focused on the microfiltration of fermentation broths after batch incubation and the mechanisms of membrane fouling by cells, debris, colloidal particles and macromolecules, e.g. for recovery of polysaccharides from fermentation broths [2]. 

There are three basic routes to produce polymers from renewable resources feedstock. Direct extraction yields polymer materials such as cellulose, starch, fibres, oils and proteins from which plastic materials can be developed. The second pathway is to convert raw materials first into biomonomers by hydrolysis, and then to polymers by chemical synthesis. A good example is PLA, the most commercialised so far. The third route is to obtain polymeric materials directly by microbial way from carbon sources through biosynthesis (fermentation). A typical example is the production of PHAs by bacteria. 

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